Atrial fibrillation (AF) is a serious public health problem because of its increasing incidence and prevalence in the aging population and its association with elevated risks of cardiovascular (CV) events and death. Our understanding of the risk factors and complications of AF is based mostly on studies that rely on its clinical recognition when a patient presents with symptoms; research on patients with cardiac implantable electronic devices indicates that a large proportion of AF episodes are not symptomatic (subclinical AF). Moreover, most studies have evaluated AF in a binary fashion-present or absent-and have not investigated AF burden (% time a person is in AF). Therefore, many knowledge gaps remain regarding AF, particularly in the elderly in whom AF exerts its greatest toll: the prevalence of subclinical AF, determinants of AF burden, and prognostic significance of AF burden all need clarification. This proposal will comprehensively define the prevalence, atherosclerosis risk factors, and clinical significance of AF and AF burden detected by a novel ambulatory ECG monitor in a biracial community-dwelling elderly cohort]. We will apply the Zio?XT Patch-an innovative non-invasive, leadless, 2-week continuous ECG recording device-to 4,000 participants (age range, 75-94 years) in the Atherosclerosis Risk in Communities (ARIC) study who will return for a planned visit 6 (V6) exam in 2016-19 and leverage the strengths of the ARIC study (extensive measurements and phenotypic data, biracial nature of the cohort, and continuous surveillance for future events) to investigate these aims: (1) [In elderly ARIC participants without a known diagnosis of AF, we will use the ECG monitor to define the prevalence of subclinical AF and AF burden, and identify subgroups with high prevalence of subclinical AF], (2) Assess the association of (a) [markers of atherosclerosis with AF and AF burden on ECG monitor in older age], (b) modifiable atherosclerosis risk factors over the previous 30 years (V1:1987-89 to V5:2011-13) with AF and AF burden on ECG monitor in older age, and (3) Quantify the relationship of AF burden in the elderly to risk of (a) [composite of nonfatal ischemic stroke, nonfatal myocardial infarction, heart failure hospitalization, and CV death], and (b) cognitive decline or dementia. [Our project may have important public health and clinical impact. First, by defining subgroups of the elderly with the highest prevalence of subclinical AF, we can target screening for subclinical AF with ambulatory ECG monitoring. Second, this project may reinforce atherosclerosis as a fundamental component in AF pathogenesis which will support a shift in strategy from one that is focused heavily on rhythm or rate management to a comprehensive one that also includes optimal control of atherosclerosis risk factors, including intensive intervention on midlife atherosclerosi risk factors to prevent AF in older age. Third, we may define AF burden as a clinically important measure, thus supporting efforts to reduce AF burden. Finally, by estimating the absolute risks of CV outcomes by different levels of AF burden, this project may elucidate the thresholds for treating AF.]